In an optical head device, light of each wavelength is focused to its approximate diffraction limit in order to perform recording reading of an optical disc. In order to obtain a focusing spot near the diffraction limit, it is necessary to set the aberration of an optical system to a small value. For this reason, strict accuracy is required for the aberration of each optical component used in an optical head device. Moreover, also for the arrangement position of each component, strict accuracy is requested in the assembly process.
As the aberration of an optical disc, there is an astigmatism or a coma aberration occurring due to deviation of the optical axis of the optical system, which is caused by an error of the arrangement position at the time of assembly or the accuracy of an optical component, or by tilt (inclination) with respect to an optical disc. These aberrations become different values in respective optical head devices due to various factors occurring in a manufacturing process even if they are optical head devices with the same optical design. In order to suppress an individual difference in such an aberration, an improvement in the accuracy of an optical component or precise assembly is necessary.
Meanwhile, a plurality of kinds of specifications including a CD with a wavelength of 785 nm and a numerical aperture (NA) of 0.45, a DVD with a wavelength of 660 nm and NA of 0.6, and a “Blu-ray” (registered trademark: hereinafter, referred to as BD) with a wavelength of 405 nm and NA of 0.85 are widely used as optical disc specifications. Generally, in the case of using an objective lens with a high NA, such as an objective lens for a BD, it is necessary to manufacture and assemble optical components more accurately than in the case of using an objective lens with an NA for a DVD, a CD, or the like.
Moreover, in order to perform recording reading of optical discs based on different specifications, a device in which a plurality of objective lenses is provided in one lens holder may be used. In such a case, however, the position of the objective lens holder is almost fixed when one optical system is adjusted. Accordingly, at the time of adjustment of other optical systems, it is necessary to perform assembly in a state where the position adjustment of an objective lens cannot be sufficiently performed.
For example, in such a case, an out-of-specification aberration may occur when focusing light on an optical disc because deviation of an optical axis occurs in other optical systems. In order to suppress such an aberration, an aberration correcting device including a liquid crystal panel which changes the phase of incident light by applying a voltage to liquid crystal in order to correct an aberration occurring in the assembly process of an optical head device has been reported (Patent Citation 1).
In addition, as another aberration correcting device which corrects a coma aberration occurring in the optical system, an aberration correcting device which corrects an aberration by generating a coma aberration component with the opposite sign to the coma aberration occurring in the optical system by performing movement adjustment of the position of one of a pair of light transmissive substrates, which have complementary curved surfaces, by the distance of Δx in a direction perpendicular to the optical axis has been reported (Patent Citation 2).